This invention generally relates to inkjet printheads, and is specifically concerned with a continuous inkjet printhead having substrate feedthroughs for accommodating power, image information and fluid conductors.
Inkjet printing has become recognized as a prominent contender in the digitally-controlled, electronic printing arena because of its non-impact, low-noise characteristics, its use of plain paper, and its avoidance of toner transfers and fixing. Inkjet printing mechanisms can be categorized as either continuous inkjet or drop-on-demand inkjet.
Continuous inkjet printing mechanisms comprise a substrate having an array of nozzles, each of which communicates with a supply of ink under pressure. The substrate has a side or face that confronts the printing medium, and which includes the outlets of each of the various nozzles. Each of the nozzle outlets continuously discharges a thin stream of ink which breaks up into a train of ink droplets a short distance from the printhead. Such printheads further include a droplet deflector for selectively deflecting droplets toward a printing medium and away from a gutter, which captures and recycles the droplets through the pressurized ink supply.
Conventional droplet deflectors impart an electrostatic charge on selected droplets which allows them to be deflected, via a repulsive charge, into the printing medium. More recently, the Eastman Kodak Company has developed thermal droplet deflectors that include an annular or semi-annular heating element circumscribing the nozzle outlets. In operation, these heating elements selectively apply asymmetric heat pulses to the stream of ink flowing out of the nozzles. These heat pulses alter the surface tension of one side of the stream of ink ejected from the nozzle outlet, thereby causing the droplet forming stream to momentarily deflect toward the printing medium. Alternatively, the printhead may be arranged so that undeflected droplets strike the printing medium, while droplets deflected by the heat pulses strike the ink gutter. The use of such heaters (which may be conveniently integrated into a silicon printhead substrate via CMOS technology) represents a major advance in the art, as far simpler to construct than conventional droplet deflectors utilizing delicate arrangements of electrostatic charging plates.
As advantageous as thermally-operated droplet deflectors are, the inventors have noted several areas where the performance of such devices might be improved. In particular, the inventors have observed that in a typical 600 nozzle per inch printhead, nearly 160 conductors are needed per inch to connect the heaters on the nozzle face to power, and the nozzles to a source of ink. While the most direct manner of installing such conductors would be to mount them directly over the nozzle face of the printhead substrate, such an installation is difficult to implement in practice due to the large number of connections and conductors and the limited area available on the nozzle face.
Generally speaking, the invention is an inkjet printhead that comprises a substrate having an interior and a flat nozzle face, at least one nozzle having an outlet in the nozzle face, an electronically-operated droplet deflector disposed adjacent to the nozzle outlet, and a plurality of feedthroughs disposed through the substrate interior for connecting the droplet deflector to power. Other feedthroughs or channels conduct pressurized liquid ink to the nozzles. The feedthroughs may include passageways disposed through the substrate interior for accommodating power and information carrying conductors connected between the droplet deflector and the power and image data circuits. The passageways may be in the form of bores extending through the interior of the substrate, and the electrical power and information carrying conductors may be either metal coatings around the surface of the bores, or metal fillings which pack the interior of the bores.
The electronically-operated droplet deflector may include a plurality of heaters circumscribing the nozzle outlets, and control circuit. Both the heaters and control circuit may be integrated into the substrate below the surface of the nozzle face via CMOS technology. The electrical conductors may be integrated in the substrate and terminate below the surface of the nozzle face. The heater control circuit applies pulses of electrical power to the heaters, which in turn generates asymmetric heat pules. The asymmetric heat pulses generate synchronous droplets and at the same time steer them toward a printing medium. In the case of symmetric heating, applied to the jet or no heat at all, the fluid is directed towards a gutter for recycling.
The use of feedthroughs throughout the interior of the printhead substrate in lieu of connections on the nozzle face of the substrate obviate the need for high, difficult-to-manufacture connector densities, and avoids unwanted surface irregularities in the nozzle face of the substrate so that it may be easily and safely cleaned by conventional wiping techniques.